VTKHDF: Support writing Partitioned data in external files
The new UseExternalComposite
option for vtkHDFWriter writes individual vtkPartitionedDatasets in different valid VTKHDF files for vtkPartitionedDataSetCollection and vtkMultiBlockDataSet. The main file containing the assembly uses external links to reference them.
vtkHDFReader has small fixes to support this usecase, but otherwise external links should be transparent for the reader, and do not require any specific processing.